A process in which pairs of chromosomes swap DNA with one another. This happens during gamete formation. A single parent cell (containing two sets of chromosomes) will form four daughter cells (with one complete set of chromosomes each). In the process of forming these daughter cells, recombination happens so that the chromosomes the daughter cells have are "mosaic," composed of different pieces of the parent cells' chromosomes. Recombination is important for evolution because it brings new combinations of genes together  a source of variation for natural selection to act upon.